[CentOS] systemd

Wed Jan 9 18:18:00 UTC 2019
Valeri Galtsev <galtsev at kicp.uchicago.edu>

On 1/9/19 11:00 AM, Simon Matter via CentOS wrote:
>> On Wed, Jan 09, 2019 at 10:43:38AM -0500, Steve Clark wrote:
>>> I am trying to understand what After= means in a unit file. Does it
>>> mean after the specified target is up and operational or only that
>>> the target has been started?
>>> I have something that needs postgres but postgres needs to be
>>> operational not just started. Sometimes it can take a bit for
>>> postgres to become operational.
>> I believe that the postgresql service has Type=notify in it's service
>> definition, which means that it will notify systemd when it is
>> operational.  This means that if you have a service that has
>> After=postgresql.service, systemd should wait until after the
>> postgresql service notifies systemd that it is operational before your
>> service will be started.
>> If your service is starting and unable to connect to postgresql, then
>> I would say that's a bug in postgresql -- it shouldn't be notifying
>> systemd that it is operational until it actually is.
> This is, in fact, one of the points why I'm very unhappy with systemd and
> the way it is implemented here and most likely in most distributions.
> Maybe things _could_ be done the right way with systemd, but it doesn't
> happen because it quickly starts to be very complex and it's a lot of work
> to do it for a complete distribution. It just doesn't happen - or at least
> did not happen in all the years since its introduction.

Yes, introduction of systemd earned Linuxes a lot of refugees. I in my 
worst times feel maybe that was the goal of it. But then I think about a 
split of refugees from Linux to UNIX descendants (FreeBSD, NettBSD etc.) 
vs to MS products, and I am not quite certain if that was a goal (though 
I do remember MS alliance with RedHat...), but if it was the goal I 
doubt refugee split was in MS favor (though one says something is better 
than nothing).

I hope, this didn't come as a rant, I should probably have used rant 
tags ;-)


> In this example, PG gets just started with "pg_ctl start" and that's it.
> Regards,
> Simon
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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247